Imagine you’re treating a patient who presented with typical cardiac chest pain. The initial ECG showed subtle lateral ST depression that seemed to resolve on subsequent ECGs. You’re very concerned by the clinical picture and believe that ACS is the likely diagnosis. However, serial troponins come back normal, even with a high sensitivity assay. This surprises you. You note that the patient is taking supplements for hair growth, and you wonder if there’s any chance this might have interfered with the test, causing false negatives. It turns out that you would be right. Read on to find out more…
Last week I was at the American Association of Clinical Chemistry Conference in Chicago (#2018AACC). I was honoured to speak alongside Fred Apple (@mrapple), Professor and Clinical Chemist at Hennepin County Medical Center and Chair of the International Federation of Clinical Chemistry (IFCC) Committee for Cardiac Biomarkers (known as IFCC-CCB for short), Allan Jaffe (Professor of Cardiology at the Mayo Clinic in Rochester and a member of the task force for the fourth universal definition of myocardial infarction), the wonderful Amy Saenger (clinical chemist at the Mayo Clinic, @asaenger10) and Torbjorn Omland (Professor of Medicine from Oslo) – all of whom have an impressive track record for their work on cardiac troponins. I was privileged to talk at what we understand was the largest ever joint industry symposium at the AACC – a collaboration between Roche, Abbott, Siemens, Beckman, Ortho and ET Healthcare. That’s six of the biggest troponin assay manufacturers in the world coming together to support medical education – which is simply amazing!
We were discussing the new IFCC-CCB practice recommendations for laboratories regarding the use of high sensitivity cardiac troponin assays, which can be found at this link.
One very topical issue is ‘biotin’. Biotin is a B vitamin, which is found in many common foods like eggs, milk, cheese and organ meats (e.g. liver). Deficiency is rare, although pregnant women get a mild deficiency fairly often, which isn’t usually symptomatic. Biotin has a role in hair and nail growth. While there is interest in taking supplements to boost hair and nail growth, there doesn’t seem to be any evidence that the supplements will work (except where there’s a biotin deficiency). There’s also some interest in using biotin for neuromuscular conditions like multiple sclerosis, but to my knowledge there’s no evidence for this as yet.
Why is this important for cardiac troponin?
OK, so if you’re not into chemistry you can skip this part. Cardiac troponin is measured using an immunoassay, which relies on the attachment of antibodies to targets on the troponin molecule. One way of ‘capturing’ the analyte you’re trying to measure is to take advantage of a very strong bond that’s formed between streptavidin and biotin – one of the strongest known non-covalent bonds. This means that a biotinylated antibody or antigen is exposed to streptavidin-coated microparticle. The assays then rely on having a method to count the number of antigen-antibody complexes that have formed in the sample. Some cardiac troponin assays rely on this principle. Unfortunately, however, if patients have high levels of biotin in their blood it can interfere with the binding process between the biotinylated antibody/antigen and streptavidin.
This can lead to falsely low levels of troponin being measured. And that’s very important when it comes to the diagnosis of acute myocardial infarction.
Has this caused any problems for patients so far?
Yes. In December 2017 the FDA issued a safety alert noting that one patient, who had been taking high dose biotin, had died after receiving falsely low troponin concentrations in a recent blood test. There are few details available but the safety report can be found in full here.
Are all troponin assays affected?
Not all troponin assays are affected. The IFCC Committee for Cardiac Biomarkers has recently published a table detailing which assays are affected, and by how much.
You can find the table at this link.
It’s essential reading for anyone who interprets cardiac troponin concentrations as part of their routine clinical practice.
What you can see from the table is that many assays are affected at extremely high concentrations (e.g. 290ng/ml), but it would be rare for patients to achieve concentrations that high – so this is unlikely to be clinically significant. Others are affected at much lower concentrations: e.g. Ortho cTnI (2.5ng/ml), Roche hs-cTnT (20ng/ml) and Siemens cTnI-Ultra (10ng/ml). Patients would usually still have to be taking extremely high doses of biotin for this interference to kick in, but that can happen in patients taking biotin supplements.
How many patients take biotin supplements at a dose that could interfere?
Dietary biotin intake is highly unlikely to interfere with troponin assays. Patients will generally need to be taking far higher doses of biotin for this to be a problem. However, if patients are taking high dose biotin supplements (e.g. for hair and nail growth) then they may have high enough levels to cause interference.
In my practice in the UK, I’ve never heard of a patient reporting that they take biotin supplements. I think it’s quite rare – unless patients simply don’t report it. However, there are reports that sales of biotin are increasing – check the link below.
What’s more, a paper just published in Clinical Biochemistry suggests that it may not be all that rare in the United States. In that work, outpatients at the Mayo Clinic were asked to report if they take biotin supplements (including biotin in multivitamins). A whopping 7.7% admitted to taking biotin supplements.
You might say that this is a highly health-conscious population. The Mayo Clinic is probably the centre of the universe for health tourism – so the outpatients there may not be your usual outpatients. However, the authors of that paper also went on to measure biotin levels in patients who presented to the ED and underwent blood testing for electrolytes. The authors found that 7.4% of patients had biotin levels above 10ng/ml – the minimum level at which interference occurs with commercially available troponin assays.
Now that sounds like a lot, and pretty scary. However, it’s worth noting some of the detail in the finer print of the paper. Only seven (of 1,449) patients in the study had biotin levels above 30ng/ml – that’s 0.5% – and this is a level where we’re really going to start getting worried about interference. So this issue might not be quite as common as the paper suggests at first sight. Importantly, however, only a small proportion of patients who were taking biotin reported it to their physicians.
What does it mean for clinicians in the ED?
There are three things that every emergency physician needs to know:
- First, you need to know what troponin assay you’re using and whether biotin may interfere with the assay. Check the IFCC table I linked to above to be sure.
- Second, if your assay is subject to interference, then remember to ask every patient about biotin intake. They may not know that they’re taking biotin – so ask about any supplements, and get the details if they are taking supplements.
- Third, if your patient is taking biotin supplements (especially at high dose) then don’t automatically trust a negative troponin result. Check with your biochemistry lab. They may recommend sending the sample out to another lab to check with another assay, or if you’re really lucky they may be able to measure biotin levels (don’t expect that to be quick though!). As getting a definitive answer may take some time, it’s important to exercise your clinical judgement. It the clinical situation means that you would have expected a high troponin result, be sure not to trust a negative result if your patient is on high dose biotin.
But, lastly, rest assured that while you need to know about this issue, it’s likely to be relatively rare in practice.